I hate to sound cryptic, but every sound, every track, every instrument, will need a different touch depending on every variable (sound, density, genre, arrangement, instrumentation).

Twist the knobs and find out what they do, then do what sounds good on any given track.

You can go from hard limiting (10:1 and up at the top volume) just to shave the clips off of a signal or gentle-to-smashing "always on" compression (VERY low threshold, -40dB or so at 1.1:1).

On attack and release, the rule of thumb is "lower is slower."

Now go play for a while.

I found a great website online , i think this link will help you...

http://computermusic.co.uk/tutorial/effects1/effects1.asp

8-)